Figure 639

Spectrum and overlap of diseases principally associated with renal papillary necrosis (RPN). Although each disease can cause RPN, it is their coexistence (darkly shaded areas) that increases the risk, which is even greater after the onset of infection (lightly shaded areas). In most cases of RPN, more than one of the conditions associated with RPN is present. Thus, in most cases, the lesion seems to be multifactorial in origin. The pathogenesis of the lesion may be considered the result of an overlapping phenomenon, in which a combination of detrimental factors appear to operate in concert to cause RPN. As such, whereas each of the conditions alone can cause RPN, the coexistence of more than one predisposing factor in any one person significantly increases the risk for RPN. The contribution of any one of these factors to RPN would be expected to differ among individuals and at various periods during the course of the disease. To the extent that the natural course of RPN itself predisposes patients to development of infection of necrotic foci and obstruction by sloughed papillae, it may be difficult to assign a primary role for any of these processes in an individual patient. Furthermore, the occurrence of any of these factors (necrosis, obstruction, or infection) may itself initiate a vicious cycle that can lead to another of these factors and culminate in RPN.